Liquid distribution unit and absorbent product having the same

ABSTRACT

A liquid distribution unit is contactively disposed directly on that surface of the liquid-permeable sheet positioned in the innermost with respect to a wearer of an absorbent product which is associated with wearer. The liquid distribution unit is provided with a plurality of liquid distribution passageways extending downward with respect to the surface thereof. The liquid distribution unit has the function of uniformly distributing and branching the liquid fed onto the surface thereof, through the liquid distribution passageways over a wide range along the surface of the surface sheet. An absorbent product having such distribution unit is provided.

TECHNICAL FIELD

[0001] The present invention relates to a liquid distribution unit whichis applied to absorbent articles such as diapers for infants and adults,sanitary items for women, and medical blood absorbents in order toimprove capabilities of the absorbents. The present invention alsorelates to a method of manufacturing the liquid distribution unit.

BACKGROUND ART

[0002] Absorbent articles for broad use in general have been developedmainly for use in disposal of urine. These absorbent articles have beendesired to be capable of handling changes caused by various factors suchas a wearer's posture, intake condition of water, and physicalcondition, for example, wearing posture and changes of discharge statessuch as amount, quality and speed of discharged urine. To securely dealwith these changes, an area and a volume sufficiently larger thannecessary on usual use conditions need to be imparted to the absorbentarticles. On the other hand, from a viewpoint of a wearer's comfort, theabsorbent articles are preferably thinner and compacter.

[0003] Considering from an aspect of absorption efficiency, theabsorbent articles, which have margins in this manner, have an absorbentwith a remarkably bad efficiency, and are also undesirable from aviewpoint of the wearer's comfort. In order to improve area and volumeefficiencies of the absorbent articles, it is important to form theabsorbent itself to be as thin and compact as possible, and further tocontrol the flow of discharged liquid. That is, a mechanism needs to bedisposed in which the discharged liquid is guided to an intended/desiredposition of the absorbent and the discharged liquid is uniformlydistributed over the whole surface of the absorbent. The absorbent ofone of the absorbent articles cannot be formed to be thinner orcompacter until these considerations are made, and there has been ademand for development of the absorbent articles which have thesecapabilities.

[0004] There have been a large number of proposals concerning thereduction of the size of the absorbent. For example, in Japanese PatentNo. 3,090,266, there is disclosed an absorbent sheet containing threecomponents including: an absorption layer mainly comprising superabsorbent polymer particles; a nonwoven fabric substrate for supportingthe super absorbent polymer particles; and a binder component forbonding the super absorbent polymer particles to one another and forbonding the super absorbent polymer particles to the nonwoven fabricsubstrate. The nonwoven fabric substrate is constituted of a nonwovenfabric which has a multilayered structure including a diffusion layer(P) formed of a fiber layer relatively high in hydrophilicity and highin density and an acquisition layer (Q) relatively low in hydrophilicityand low in density. On the surface of the absorbent sheet, an absorptionregion phase (phase A) including the absorption layer and the nonwovenfabric substrate carrying the absorption layer, and adiffusion/acquisition region phase (phase B) in which the superabsorbent polymer particles hardly exist and which is mainly formed ofonly the non-woven substrate are distributed so that the phases can bedistinguished from each other.

[0005] Moreover, in Japanese Patent Application Laid-Open No.2000-232,985, there is described a disposable incontinence liner inwhich an absorption sheet is disposed between a top sheet and backsheet. For the absorption sheet, there is described an absorbent sheetincluding: an absorption layer in which polymeric absorbent particlesare bonded by microfibrillated fine fibers; and a sheet support materialfor supporting this absorption layer. The polymeric absorbent particleshaving specific weights, and the absorbent sheet having specificthickness and rigidity/softness are used.

[0006] Further in Japanese Patent No. 2,872,851, there is disclosed anabsorbent article including a surface material having permeability toliquid, an absorbent having liquid holding property, and a leakpreventive material having impermeability to the liquid. A part or allof the absorbent is constituted of an absorption sheet in whichpolymeric absorbent particles are fixed to an absorption material by anadhesive applied in a dot, linear, or curve form. For the adhesive, a180° peeling adhesive force (JIS C2107) is not less than 500 g and notmore than 4000 g. An occupying area of the applied adhesive is not lessthan 10% and not more than 70%.

[0007] Moreover, a absorbent sheet in which polymeric absorbentparticles are mixed in high concentration in a so-called air-laid methodof molding a pulp sheet by a dry process and bonded/integrated by aheat-melting binder also starts to be used in an ultrathin absorbentarticle.

[0008] However, although the absorbent article using the above-describedabsorbent sheet is thin and compact as compared with the conventionalarticle, further improvement is still necessary with respect to theefficiency.

[0009] Additionally, as a measure for efficiently absorbing thedischarged liquid into the thin absorbent, a bulky nonwoven fabric hasheretofore been added as a diffusion sheet, distribution sheet, transfersheet, or acquisition sheet to the surface of the thin absorbent. Thesecommon ideas are based on the use of the diffusion phenomenon of theliquid using capillaries among the constituting fibers. An attempt hasalso been made to dispose a foam or bulky opening film subjected to asurface hydrophilic treatment for temporarily trapping the liquidbetween a top sheet and the absorbent or in the absorbent.

[0010] The present invention has been derived from an attempt to purelyincorporate a mechanical liquid distribution mechanism which is disposedin contact with a discharge port of body fluid into the absorbentarticle.

DISCLOSURE OF THE INVENTION

[0011] An object of the present invention is to provide a distributionunit capable of distributing a liquid discharged from a wearer into thesurface of an absorbent.

[0012] According to one aspect of the present invention, there isprovided a liquid distribution unit disposed to keep in contact with thesurface of a liquid permeable sheet of an absorbent article disposed ina contact position with respect to a wearer on the wearer's side.

[0013] The liquid distribution unit includes a plurality of liquiddistribution passages in a hanging direction with respect to the surfaceof the unit, and the liquid distribution unit divides and branchesfinely the liquid supplied to the surface of the unit along the surfaceof the surface sheet.

[0014] The liquid distribution unit may include a plurality of openings,and introductory tubes extending toward the surface of an absorbentmember from the openings, and may be formed so as to guide the liquidfrom the openings toward the surface of the absorbent member through theintroductory tubes.

[0015] For each opening, preferably, when its opening surface isapproximated to an ellipse, its long axis is at least 0.5 mm, its shortaxis is 10 mm at maximum, its open area ratio is not less than 10% andnot more than 90%. The number of openings is preferably at least 200openings per 100 cm².

[0016] The length of the introductory tube is preferably not less than0.50 mm and not more than 5 mm.

[0017] The introductory tube forming a funnel shape, which has a largeinlet diameter on its opening surface side and a small outlet diameter,is advantageous.

[0018] The liquid distribution unit can be constituted of athermoplastic film having a thickness which is not less than 10 μm andnot more than 100 μm.

[0019] For the liquid distribution unit, wettability may also beimproved by treatment of the surface of the unit with a hydrophilicagent, and mobility of the liquid from the opening is improved in thiscase.

[0020] Moreover, the absorbent member includes a plurality of absorbentsheets laminated upon one another, and the liquid distribution unit mayinclude a portion exposed onto the absorbent sheet positioned in a toplayer, and a portion extending to reach the absorbent sheet positionedin a lower layer of the absorbent sheet of the top layer.

[0021] According to the present invention, there is further provided anabsorbent article including the above-described liquid distributionunit. In this case, the absorbent article includes a liquid permeablesurface sheet positioned on an inner side with respect to a wearer'sbody in a wearing state; a liquid impermeable sheet positioned on anouter side from the surface sheet; and an absorbent member containingsuper absorbent polymer particles as a major component disposed betweenthe surface sheet and the liquid impermeable sheet. The liquiddistribution unit is disposed between the body surface of the wearer andthe absorbent member.

[0022] The absorbent member for use preferably contains at least 50% byweight or more of the super absorbent polymer particles.

[0023] A liquid permeable nonwoven fabric may further be disposed on theliquid distribution unit.

[0024] A ratio of an area occupied by the liquid distribution unit withrespect to the total area of the surface sheet is preferably not lessthan 5% and not more than 50%, and the unit is partially disposed so asto have an area of at least 10 cm².

[0025] The liquid permeable nonwoven fabric may further be disposed onlyon the partially disposed liquid distribution unit.

[0026] Furthermore, an acquisition layer or diffusion layer may bedisposed under the liquid distribution unit. In order to broadlydistribute and diffuse the liquid in a surface part, a liquidimpermeable sheet is sometimes disposed in the lower surface of theliquid distribution unit to partially block an outlet of thedistribution unit.

[0027] The absorbent member constituted of the absorbent sheet includinga nonwoven substrate, super absorbent polymer particles, andmicrofibrillated cellulose can be used.

[0028] Alternatively, the absorbent member may also be constituted ofthe absorbent sheet including a wood pulp obtained by a so-calledair-laid method, super absorbent polymer particles, and bondingmaterial.

[0029] The absorbent member has a retained absorption amount of 300 ccor more. When a water absorption speed is measured every 100 cc at aninterval of ten minutes three times, the water absorption speed is 60sec or less in any measurement, and a deviation among the threemeasurement data is suitably 30 sec or less.

[0030] Furthermore, the absorbent sheet has a bent shape whosetransverse section has a Z-shape, the liquid distribution unit isdisposed only in a center portion of the upper surface of the absorbentsheet, and the unit can be used in this mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a perspective view showing a cut part of a liquiddistribution unit according to one embodiment of the present invention;

[0032]FIG. 2 is a vertical sectional view of a part of the liquiddistribution unit shown in FIG. 1;

[0033]FIG. 3 is an explanatory view showing the principles of liquiddistribution in the liquid distribution unit of the present invention;

[0034]FIG. 4 is an explanatory view showing a mechanism of liquiddistribution occurring between the liquid distribution unit of thepresent invention and an absorbent disposed under the unit;

[0035]FIG. 5 is an enlarged view of a part shown by V of FIG. 4;

[0036]FIG. 6 is a perspective view showing a part of the liquiddistribution unit according to another embodiment of the presentinvention;

[0037]FIG. 7 is a vertical sectional view showing a shape of a tubeportion applied to the liquid distribution unit of the presentinvention;

[0038]FIG. 8 shows plan views showing different modes of liquiddistribution unit arrangement of the present invention to be combinedwith an absorbent member;

[0039]FIG. 9 is a vertical sectional view schematically showing anabsorbent part of an absorbent article according to the presentinvention including the liquid distribution unit;

[0040]FIG. 10 shows vertical sectional views schematically showing theabsorbent parts of different conventional absorbent articles;

[0041]FIG. 11 is a vertical sectional view in a width direction, showinga constitution example of the absorbent member applied to the absorbentarticle of the present invention;

[0042]FIG. 12 is a vertical sectional view in a width direction, showinganother constitution example of the absorbent member applied to theabsorbent article of the present invention;

[0043]FIG. 13 shows plan views showing different bonding modes of abonding portion for bonding the liquid distribution unit of the presentinvention with respect to the absorbent member;

[0044]FIG. 14 is a perspective view showing another mode of theabsorbent combined with the liquid distribution unit of the presentinvention; and

[0045]FIG. 15 is a vertical sectional view of FIG. 14.

BEST MODE FOR CARRYING OUT THE INVENTION

[0046] A liquid distribution unit of the present invention will bedescribed hereinafter in detail with reference to the drawings.

[0047]FIG. 1 is a model diagram showing one example of the liquiddistribution unit according to the present invention. A liquiddistribution unit 100 includes a liquid impermeable sheet 11 having alarge number of openings, and a large number of tubular introductorytubes 12 extending in a direction hanging from the surface of the liquidimpermeable sheet 11. To simplify the description, in FIG. 1, a largenumber of circular openings 13 are formed in the liquid impermeablesheet 11. The introductory tube 12 having an inner diametersubstantially equal to a diameter of the opening 13 is disposed so thatan axial center of the introductory tube 12 agrees with a center of theopening 13. In the corresponding position, the tube is connected to thelower surface of the liquid impermeable sheet 11. This opening 13 and acenter hole of the introductory tube 12 form a liquid distributionpassage 20.

[0048]FIG. 2 shows an enlarged sectional view of a part of the liquiddistribution unit 100 shown in FIG. 1. In the figure, the thickness ofthe liquid impermeable sheet 11 is shown by t, the diameter of theopening 13 is shown by φ, and the length of the introductory tube 12 isshown by H.

[0049] A mechanism for distributing the liquid in the liquiddistribution unit of the present invention will be describedhereinafter.

[0050] In the present invention, as shown in FIG. 3, the term of “thedistribution of the liquid” means a phenomenon in which a flow A of theliquid which has entered via an upper inlet is discharged as a pluralityof mechanically divided flows A1, A2, A3, . . . An in going out of loweroutlets.

[0051] As shown in FIG. 4 and FIG. 5 showing a part of FIG. 4 in anenlarged size, when the divided flows Al to An collide with the surfaceof an absorbent S, the flows are further divided into flows B1 and B2 .. . Bn absorbed by the absorbent S and flows C1, C2 . . . Cn overflowingto spaces P along the surface in accordance with flow amount and speed.The flow which overflows in the space P having a height H and width Lformed in the liquid distribution unit 100 and the surface of theabsorbent S is absorbed into the absorbent S with a flow shown by D1.

[0052] In this manner, the flow A is formed into the divided flows A1,A2 . . . An, and is further multi-divided into B1, B2 . . . Bn, C1, C2 .. . Cn, and D1, D2 . . . Dn, and the finely divided flows are suppliedinto the absorbent S. As a result, the irregularly discharged liquid isformed into the controlled fine flow by a mechanical distributioneffect, and rapidly spreads over the surface of the absorbent by thedistribution effect. Only a part of the absorbent S is prevented fromlocally swelling, and it is possible to effectively use the wholesurface of the absorbent S. To impart such a uniform surface diffusioneffect is especially important for the absorbent containing superabsorbent polymer (SAP) particles at a high ratio, which hascharacteristics that the thickness is small and capacity is large butabsorption speed is low.

[0053] As clear from the above description, the following basicconditions are necessary for the liquid distribution unit of the presentinvention to fulfill the desired functions.

[0054] (1) To distribute the liquid, the distribution unit needs to havean ability to retain a certain liquid amount. For this, it is importantto dispose a space having a height H and width L in an appropriate sizein FIG. 5 between the liquid distribution unit and the surface of thesurface sheet positioned under the unit.

[0055] (2) It is necessary to have an introduction function of movingthe liquid from the opening to introduce the liquid into the absorbentsurface.

[0056] (3) An isolating distance (corresponding to the length H of theintroductory tube) for isolating the opening from the surface sheet isrequired.

[0057] (4) A space (P) needs to exist between the introductory tubesdisposed adjacent to one another. For the space, in a structure in whichthere is not any introductory tube, for example, in a structure in whichthe opening is disposed in a thick sheet, this space is not generated,and therefore the function aimed of the present invention is notobtained. When the introductory tube becomes thinner and has a longerlength (H), the space becomes larger.

[0058] (5) To maintain stability of the shape, that is, to obtaincharacteristics that the liquid distribution unit is not deformed orcollapsed even under loads such as a wearer's weight, it is importantthat the liquid impermeable sheet for use in the liquid distributionunit has a certain degree of thickness. The thickness also depends onthe material which constitutes the liquid impermeable sheet. However, itis desirable to have a thickness of at least 10 μm or more, morepreferably 20 μm or more.

[0059] This will be described with reference to FIG. 2. When thetransverse sectional shape of the introductory tube 12 is circular, thediameter φ indicates a value of 0.5 mm or more, preferably 1 mm to 10mm, the length H is 0.5 mm or more, preferably 1 mm to 10 mm, and thethickness t of the liquid impermeable sheet is 10 μm or more, preferably20 μm to 200 μm.

[0060] As the material constituting the liquid distribution unit, thematerial having an absorbing property entirely like the nonwoven fabricwhich has heretofore been used as an acquisition layer or diffusionlayer is not therefore used in the liquid distribution unit according tothe present invention because the material itself absorbs the liquid.The material itself may be impermeable to the liquid so that the liquidis retained as little as possible. On the other hand, a metal plate issatisfactory both in shape stability and distribution effect, but isexcessively high in rigidity, and it is difficult to apply the metalplate to the absorbent article. The appropriate material, for example,is a thermoplastic film or a bonded material of the film with thenonwoven fabric. Examples of the material include: a single-layer filmof a simple substance or a blend material of a thermoplastic syntheticresin such as PE, PP, PET, EVA, MA, MMA; a co-extrusion film such asPE/PP, PE/PET, low melting point PET/PET, and EVA/PE; and a bondedmaterial of the single-layer film, co-extrusion film, and nonwovenfabric such as a spun bond nonwoven fabric, thermal bond nonwovenfabric, and tissue. The thickness of the film is 10 μm or more, andpreferably 100 μm or less, because a problem occurs in moldability ofthe opening with an excessively large thickness. It is to be noted thatin order to reduce the liquid remaining in the surface locally, asurface hydrophilic treatment is permitted for improvement of surfacewettability, and is sometimes rather desirable to facilitate themovement of the liquid from the opening. For the hydrophilic agent,measures are taken such as the coating with an anionic, cationic, ornonionic surfactant and the mixing of the hydrophilic components such asPEG in a material polymer itself to impart hydrophilicity.

[0061] In order to industrially produce such a structure, for example,any of the following methods would preferably be used.

[0062] (1) A method of using a metal mold to extrude plastic resindirectly from a molding machine and molding the distribution unit. Inthis method, it is necessary to form a smooth and flexible moldedmaterial without any protrusion or surface damage.

[0063] (2) A method of forming a concave/convex portion in a net formedof plastic filaments having a certain degree of rigidity bythermoforming. In this thermo-formed material, the concave portionfunctions as the opening, and the convex portion functions as theintroductory tube. In this case, the net needs to have a mesh size tosuch a degree that the liquid can sufficiently pass through the net. Forexample, the size is preferably 40 meshes to 100 meshes.

[0064] (3) A method of forming a deep dent in a liquid impermeableplastic film by thermoforming and opening the bottom of the dentmechanically or further by a heat treatment.

[0065] (4) A method of forming a deep embossed groove in a plastic filmand heating and vertically/laterally drawing the film to produce anopening in the bottom of the groove.

[0066] (5) A method of guiding a plastic film in a heated state into aporous surface cylinder whose inner pressure is reduced, applying heatair to the film to suck the film, and forming an opening in accordancewith the pore size of the cylinder to obtain a molded material to whichthe introductory tube is also formed in accordance with the thickness ofthe porous cylinder.

[0067] The shape of the opening and arrangement example of the liquiddistribution unit obtained in the above method (4) or (5) are shown inFIG. 6.

[0068] In order to effectively perform the fine division of the liquid,it is important to appropriately control the state of the opening whichis the inlet of the liquid.

[0069] The opening state is represented by the opening shape, the numberof openings, opening ratio (open area ratio), and the like.

[0070] The opening shape may be any of circular, elliptic, square,rectangular, quadrangular, and hexagonal shapes. However, when the sizeof the opening is excessively small, the movement efficiency of theliquid is bad. Conversely, when the size is excessively large, a liquiddivision effect worsens.

[0071] When the opening shape is approximated to an elliptic shape andits long axis is less than 0.5 mm, surface tension acts, and the passageof the liquid is inhibited. A preferable long axis size is not less than1.0 mm. On the other hand, when the size is excessively large, a passingproperty of the liquid becomes satisfactory, but the division effectworsens, and therefore the short axis size is 10 mm at maximum,preferably 5 mm at maximum.

[0072] The number of openings also largely influences the divisioneffect. When the number of openings per unit area is small, it isnecessary to have a large opening area of each opening, and the divisionefficiency worsens for the above-described reason. Therefore, the numberof openings is at least 200 per 100 cm², preferably at least 500 per 100cm².

[0073] The area of openings represents an open area ratio at a time whenthe total area of the distribution unit is assumed to be 100. Zero %indicates that there is not any opening. The open area ratio ispreferably 10% or more, more preferably 90% or less. When the open arearatio is less than 10%, the movement speed of the liquid is excessivelylow. When the open area ratio exceeds 90%, the shape stability of theliquid distribution unit becomes worse, and so the open area ratio ispreferably in a range of 20% to 80%.

[0074] In the above description, there is also a cylindricalintroductory tube having a circular transverse section, but in thepresent invention, an introductory tube having a shape other than thecylindrical shape can be applied. Some examples are shown in FIGS. 7(A),7(B), 7(C). An introductory tube 12 a shown in FIG. 7(A) has a truncatedconical shape whose end being in contact with the opening of the liquidimpermeable sheet 11 has a small diameter and which successivelyenlarges toward an end on a distant side. An introductory tube 12 bshown in FIG. 7(B) has a shape vertically reverse to that of theintroductory tube 12 a of FIG. 7(A). Furthermore, an introductory tube12 c shown in FIG. 7(C) has a cylindrical shape having an equal diameterdown to a position corresponding to approximately the half of the lengthfrom an upper end, a lower connected portion has a truncated conicalshape, a conical insert 12 d is disposed in a truncated conical space,and the liquid passage in this portion is annular.

[0075] It is possible to apply introductory tubes having various shapes,but in many cases the shape of FIG. 7(B) is preferred because the shapehas advantages that the tube is easily formed and there is littlereverse flow of the liquid.

[0076] The length (H) of the introductory tube is an important factorfor determining the capacity of the passage. The longer tube ispreferred but becomes thick. It is therefore necessary to adequatelyselect the length. The length (H) is preferably not less than 0.5 mm andnot more than 10 mm, and further preferably 1.0 mm to 5 mm.

[0077] The liquid distribution unit of the present invention is attachedto the absorbent article so as to cover all or part of the surface ofthe absorbent disposed closely to a wearer's skin (hereinafter referredto as the “upper surface”). In many absorbent articles, the uppersurface of the absorbent is covered with a liquid permeable sheet (i.e.,the top sheet) obtained by hydrophilic-treatment of a nonwoven fabriccontaining synthetic fibers such as PE, PP, PET which are majorcomponents. The liquid distribution unit of the present invention ispreferably disposed on the surface sheet, that is, an outermost surface.When the top sheet is not disposed and the acquisition layer is disposedin the outermost surface, the unit is disposed on the acquisition layer.In the case of using an absorbent sheet composed of a substrate andsuper absorbent polymer particles, the substrate sometimes has a topsheet or acquisition effect. In this case, the liquid distribution unitis disposed so as to directly come in contact with the absorbent sheet.However, when the surface sheet is closely attached or bonded to theliquid distribution unit by an appropriate measure, and even when theunit is disposed right under the surface sheet, the unit is disposedsubstantially in the vicinity of the skin, and this is thereforeincluded in the scope of the present invention.

[0078] The liquid distribution unit of the present invention has afunction of controlling the distribution of body fluid, and thereforeneeds to be disposed in the vicinity of a body fluid discharge port, butthe area, which can sufficiently cover the discharge port portion, issufficient. It is unnecessary to cover all the large area of theabsorbent member. When the absorbent member entirely covered with thesurface sheet is assumed, the covering of the half (50%) of the surfacesheet at maximum is sufficiently enough for the necessary area of theliquid distribution unit. Also considering from economy of the article,the area, which is not less than this size, is totally useless. However,the area needs to be about at least 3%, and a concretely necessary areaof the absorbent article would be 10 cm² or more.

[0079] In this manner, since the liquid distribution unit needs to comein contact with the discharged body fluid as directly as possible, it isimportant to dispose the unit in the vicinity of the body fluiddischarge port. Therefore, it is also necessary to change the disposedposition in accordance with uses for men, women, adults, and childrendepending on the circumstances.

[0080] Table 1 shows a result of a test for measuring a change of anabsorption speed with respect to an occupied area of the liquiddistribution unit on the outermost surface. We adopted as thedistribution unit an opening film (trade name “X-27373”, thickness of1184 μm) manufactured by Tredegar Co. 100 ml of a physiological saltsolution was supplied via a nozzle having a nozzle diameter of 2 mm, andabsorption time was measured to carry out the test. While a positionalrelation between the liquid distribution unit and absorbent member wasset as shown in FIG. 9 described later, an experiment was carried out.It is seen from the result of Table 1 that a system not including thedistribution unit requires 170 sec, while the absorption-time is reducedto about ⅕ or less in a system including the distribution unit. When theoccupied area is not less than 20 cm² as the cover area of the liquiddistribution unit, the absorption speed is seen to be hardly influenced.It is to be noted that a discharge speed of urine by a healthy baby oradult is 60 sec or less per 100 ml. When the absorbent article isconsidered, for the whole absorption ability, in terms of a retentionamount (retained absorption amount), the article is generally designedto have a retained absorption amount of 300 ml or more. It is alsoimportant to reduce the absorption speed to 60 sec or less, preferably40 sec or less per 100 ml.

[0081] This experiment result is a proof indicating that thedistribution unit of the present invention is based on a physicalmechanism which is different from the so-called acquisition effect. Thedegree of aquisition effect becomes nearly proportional to the occupiedarea. TABLE 1 Occupied Area and Absorption Speed of Distribution UnitExp. Exp. Control Exp. 1 Exp. 2 Exp. 3 4 5 Area of liquid 0 10 20 40 100350 distribution unit (cm²) Occupying ratio 0 2.9 5.7 11.4 35 100 intotal surface area of absorbent member (%) Absorption speed 170 35 28 3029 30 of 100 ml artificial urine (sec)

[0082] In the present invention, with the use of a liquid distributionunit having an area only covering only a part of the total surface ofthe surface sheet of the absorbent, its plane shape changes inaccordance with a targeted capability, or various conditions of a usemode. Some shapes are shown in FIGS. 8(A) to 8(E). In these figures,reference numeral 30 denotes the absorbent member of the absorbentarticle, and the liquid distribution unit 100 of the present inventionis disposed on the top sheet. The liquid distribution unit 100 has avertically long rectangular shape in the example of FIG. 8(A), and has alaterally long rectangular shape in the example of FIG. 8(B). The liquiddistribution unit 100 may have various shapes such as an elliptic shapeas shown in FIG. 8(C), a triangular shape as shown in FIG. 8(D), and aconvex shape as shown in FIG. 8(E).

[0083] The absorbent part of the absorbent article including the liquiddistribution unit of the present invention basically includes theabsorbent member, and the liquid distribution unit disposed on theabsorbent member. The absorbent member may also include a usualstructure constituted of a laminate material of super absorbent polymerparticles and pulp, and a cover sheet with which the laminate materialis covered, but preferably has a large content of super absorbentpolymer particles. The absorbent member is preferably a pulp-lessultrathin absorbent sheet including a support sheet and an absorbentlayer supported on the surface of the support sheet and containing thesuper absorbent polymer particles as a major component. The majorcomponent indicates an occupying state of 50% or more, preferably 60 to90% of the total component weight involved in the absorption.

[0084]FIG. 9 shows the structure of an absorbent part in an absorbentarticle including an absorbent member 40 and liquid distribution unit100. For the sake of simplicity, other accessory elements such as a backsheet and bonding unit are omitted. In this embodiment, in the absorbentmember 40, there are disposed: a first absorbent sheet 43 including aliquid permeable support sheet 41 and strip-shaped absorption layers 42disposed in parallel with one another on the lower surface of thesupport sheet; and a second absorbent sheet 46 which is disposed underthe first absorbent sheet and which includes a layer of super absorbentpolymer particles 45 on the lower surface of a support sheet 44. Theabsorbent member 40 includes a top sheet 47 disposed on the firstabsorbent sheet 43, and the liquid distribution unit 100 is disposed onthe top sheet.

[0085] The liquid distribution unit 100 has an about 50 cm² rectangularshape whose area is largely smaller than an area of 300 cm² of theabsorbent member 40, and is disposed substantially in a center part ofthe absorbent member 40 as shown in FIG. 8(A).

[0086] A test was carried out to compare an absorption capability of theabsorbent article including the liquid distribution unit of the presentinvention as shown in FIG. 9 with that of three types of controlsamples. The result is shown in the following Table 2.

[0087] The structures of comparative samples are shown in FIGS. 10(A),10(B), and 10(C). Sample No. 1 has a structure of FIG. 10(A) excludingthe liquid distribution unit 100 from the absorbent article of thepresent invention; sample No. 2 includes a structure of FIG. 10(B) inwhich instead of the liquid distribution unit 100, an acquisition layer110 formed of an air-laid nonwoven fabric is disposed between the topsheet 47 and absorbent member 40; and sample No. 3 includes a structureof FIG. 10(C) in which instead of the liquid distribution unit 100, anacquisition layer 120 formed of a thermal bond nonwoven fabric isdisposed over the whole surface between the top sheet 47 and absorbentmember 40. TABLE 2 Comparison of Absorption Speeds ComparativeComparative Comparative sample No. 1 sample No. 2 sample No. 3 Presentinvention First Second First Second First Second First Second Thirdabsorp- absorp- absorp- absorp- absorp- absorp- absorp- absorp- absorp-tion tion tion tion tion tion tion tion tion Weights of liquiddistribution — — 100 100 50 50 38 38 38 unit or acquisition layer(g/cm²) Thickness of liquid distribution — — 1 1 0.6 0.6 1 1 1 unit oracquisition layer (mm) Thickness of absorbent member (mm) 0.6 0.6 1.71.7 1.5 1.5 0.6 0.6 .06 Relative ratio of total thickness 40 40 113 113100 100 47 47 47 (%) (on basis of sample No. 3) (Standard) Open arearatio (%) — — — — — — 30 30 30 Number of openings of liquid — — — — — —1400 1400 1400 distribution unit open- open- open- (Openings/100 cm²)ings ings ings Use area of liquid distribution — — — — — — 50 50 50 unit(cm²) Absorption speed 150 200 22 45 25 55 20 25 24 (Absorption time of100 ml/sec) Total absorption volume (ml) 100 200 100 200 100 200 100 200300

[0088] Although the liquid distribution unit of the present inventionhas a small installation area of 50 cm², it is seen that an absorptionspeed promotion effect equal to or more than that of the conventionalacquisition material disposed over the entire surface is provided.Especially when the measurement is repeated twice, three times, theabsorption speed largely drops in the conventional constitution.However, it is seen that with the use of the liquid distribution unit ofthe present invention, the speed is nearly the same even in the thirdabsorption.

[0089] From the above test result, for the absorbent article includingthe liquid distribution unit of the present invention, while theabsorption capability is enhanced, it is possible to largely reduce theentire thickness.

[0090]FIG. 11 is a vertical sectional view in a width direction showinga structure of the absorbent member 40 according to another exampleapplied to the absorbent article of the present invention. For the sakeof simplicity, the other accessory elements such as the back sheet andbonding unit of the absorbent article are omitted. In this example, afirst absorbent sheet 43 includes a liquid permeable support sheet 41and strip-shaped absorption layers 42 disposed in parallel with oneanother on the lower surface of the support sheet. Under this firstabsorbent sheet, a second absorbent sheet 46 is disposed including alayer of super absorbent polymer particles 45 disposed on the lowersurface of the support sheet 44. The first absorbent sheet 43 is widerthan the second absorbent sheet 46, and opposite side portions extendingoutwards from opposite edges of the second absorbent sheet 46 have ashape bent so as to have a Z-shaped transverse section. Moreover, theliquid distribution unit is disposed on the first absorbent sheet 43 inthe middle part of the absorbent member 40 in the width direction.

[0091] In this constitution, the liquid supplied to the absorbent member40 from above is branched/distributed by the liquid distribution unit100, rapidly absorbed in a broad region in the surface of the firstabsorbent sheet 43, and further absorbed by the second absorbent sheet46. The Z-shaped portion disposed on the side of the first absorbentsheet swells and rises in response to the absorption, and also has afunction of a side bank for preventing sideward leak.

[0092] Furthermore, FIG. 12 shows a constitution in which the firstabsorbent sheet 43 includes an elongated middle portion 43 a and a pairof elongated side portions 43 b positioned on opposite sides of themiddle portion. These portions are disposed on the second absorbentsheet 46, and further the liquid distribution unit 100 is combined withthem. In this example, the liquid distribution unit 100 has a widthsubstantially equal to that of the absorbent member 40, and ispositioned on the first absorbent sheet 43 a in the middle part of thewidth direction, but the opposite side portions of the unit extendbetween the first absorbent sheet 43 a and the second absorbent sheets43 b and are disposed under the second absorbent sheets 43 b. It is tobe noted that, in this example, the top sheet 47 is disposed on theliquid distribution unit 100.

[0093] In this constitution, the liquid supplied to the absorbent member40 from above is branched/distributed by the liquid distribution unit100, rapidly absorbed in the newly whole region in the surface of thefirst absorbent sheet 43, further guided under the second absorbentsheets 43 b by the liquid distribution unit 100, and furthersubstantially simultaneously absorbed by the second absorbent sheet 46.Therefore, the unit is suitable especially for the absorbent structuressuch as diapers for children which deal with a large amount of liquid ina short time. It is to be noted that the lateral width of thedistribution unit needs to be broadened, but the vertical width may benarrow.

[0094] The mode in which the liquid distribution unit is bonded to thetop sheet and/or directly to the absorbent is important because thedivision effect of the liquid is influenced. For example, the entirebonding of the unit by hot melt and the closing of distribution outletshave to be avoided. FIGS. 13(A), 13(B), 13(C), and 13(D) show examplesin which the substantially rectangular liquid distribution unit 100 isbonded to the surface sheet of the absorbent member 30 in differentportions. The unit is bonded by a bonding portion 101 over the entirefour sides of the liquid distribution unit 100 in a sample S-1 as shownin FIG. 13(A), but the unit is bonded only in two long sides of theliquid distribution unit 100 in a sample S-2 as shown in FIG. 13(B), theunit is bonded in only two short sides of the liquid distribution unit100 in a sample S-3 as shown in FIG. 13(C), and the unit is bonded inthe bonding portions 101 only in four corner portions in a sample S-4 asshown in FIG. 13(D).

[0095] A test was carried out to check an influence of differences ofthese bonded states onto the absorption capability of the absorbent. Theexperiment was carried out by measurement of the absorption time of 100ml of liquid with respect to each sample in a method similar to theabove-described method, and the result is shown in Table 3. TABLE 3Fixing Method of Distribution Unit and Absorption Time of Liquid SampleS-1 S-2 S-3 S-4 Absorption speed (sec) 58 42 38 30

[0096] For the sample S-1 bonded in all the four sides, even when theliquid was distributed, the distribution effect in the longitudinal andlateral directions remained only in the distribution unit area.Subsequently, the effect shifted inwards from the surface of theabsorbent member 30. Therefore, the absorption required 58 seconds. Forthe S-4 partially fixed only in four corners, there were outlets in fourdirections, and therefore the liquid also diffused to the outside of thedistribution unit in the longitudinal and lateral directions. Theabsorption ended in 30 seconds. Needless to say, when the liquiddistribution unit was not used, the absorption required 150 sec to 180sec. Therefore, even when the liquid distribution unit is bonded in alledges, the installation effect of the unit is large. However, attentionsneed to be paid to the change of the capability even with a fixing mode.Moreover, even when the liquid shift of the absorbent surface iscontrolled in the lower surface outlet of the liquid distribution unit,the surface diffusion state can be changed. That is, when the lowersurface of the distribution unit is partially blocked by the liquidimpermeable sheet, the absorption portion of the absorbent may bechanged.

[0097]FIG. 14 is a perspective view and FIG. 15 is a vertical sectionview. They show an example of the 100 mm×100 mm liquid distribution unit100 laid on a 160 mm×250 mm absorbent member 30. In the unit, only a 50mm×80 mm portion in the middle part is covered with a liquid impermeablesheet 50 formed of a PE film having a thickness of 30 μm, and thetransfer of liquid into the absorbent member 30 is blocked in theportion. Accordingly, the liquid diffuses more broadly and speedily inthe surface and is absorbed by the absorbent member 30 so that the wholeabsorbent is uniformly used.

[0098] In examples of FIGS. 14 and 15, a liquid impermeable sheet 50 ofPE film is combined to the lower surface of a liquid distribution unit100 by an adhesive, but may also be bonded on the side of an absorbent30 or to the surface sheet (not shown). For the liquid impermeable sheet50 for partially blocking the outlets of the liquid distribution unit, afilm of as PE, PP, nylon, or PET, a water-resistant nonwoven fabric suchas SMS, or a water-soluble PVA film, which temporarily has resistance towater but is melted away, is prepared in an appropriate area and shapein accordance with the area of the liquid distribution unit 100, andcombined in an appropriate position. Accordingly, the transfer directionand state of the flow of the liquid which goes out can freely becontrolled.

[0099] As described above, in the liquid distribution unit of thepresent invention, the body fluid irregularly discharged in the surfaceof the unit is divided and branched finely, along the surface of thesurface sheet of the absorbent positioned below the unit by themechanical distribution effect by a large number of liquid distributionpassages. Accordingly, the liquid forms a controlled fine flow andrapidly spreads over the absorbent surface, only a part of the absorbentis prevented from locally absorbing/swelling, and the absorptioncapability of the absorbent can effectively be used.

[0100] Furthermore, in the absorbent article of the present inventionincluding the above-described liquid distribution unit, the absorptioncapability of the used absorbent is fulfilled at the maximum to realizethe enhancement of the capability of the absorbent article.

INDUSTRIAL APPLICABILITY

[0101] Liquid distribution units of the present invention improveabsorption capabilities of absorbent articles such as diapers forinfants and adults, sanitary items for women, and medical bloodabsorbents. Therefore these absorbent articles are produced in largeamounts and are broadly used.

1. (Amended) A liquid distribution unit disposed in a position betweenan absorbent member containing super absorbent polymer particles as amajor component and a wearer's body, said liquid distribution unitcomprising a plurality of liquid distribution passages which extend in ahanging direction with respect to the surface of the unit and whose endsare in contact with said absorbent member, and having a function ofbranching a liquid supplied to the surface along the surface of saidabsorbent member through each of the liquid distribution passages andaccordingly of dividing and distributing the liquid along the surface ofthe absorbent member, and being disposed in a position as near aspossible to said absorbent member.
 2. The liquid distribution unitaccording to claim 1, wherein said liquid distribution passages comprisea plurality of openings; and introductory tubes extending toward thesurface of the absorbent member from each of the openings, and furtherhaving a function of guiding the liquid which has flown from each of theopenings through these introductory tubes toward the surface of theabsorbent member.
 3. The liquid distribution unit according to claim 2,wherein each of the openings approximated to an ellipse has a shortdiameter of at least 0.5 mm and a long diameter of 10 mm at maximum, theopen area ratio of the openings is in a range of 10% to 90%, and thenumber of the openings is at least 200 per 100 cm².
 4. The liquiddistribution unit according to claim 2 or 3, wherein each of theintroductory tubes has a funnel shape with an outlet diameter smallerthan an inlet diameter.
 5. The liquid distribution unit according to anyone of claims 2 to 4, wherein the length of each of the introductorytubes is in a range of 0.50 mm to 10 mm.
 6. The liquid distribution unitaccording to any one of claims 1 to 5, which is constituted of athermoplastic film having a thickness in a range of 10 μm to 100 μm. 7.The liquid distribution unit according to any one of claims 2 to 6,which is improved in surface wettability by treatment of the surface ofthe liquid distribution unit with a hydrophilic agent, and accordinglyis improved in mobility of the liquid from each of the openings.
 8. Theliquid distribution unit according to any one of claims 1 to 7, whereinthe absorbent member comprises a plurality of absorbent sheets laminatedupon one another, and the liquid distribution unit includes a portionexposed onto the surface of a top layer of the laminated absorbentsheets, and a portion extending to reach an absorbent sheet positionedin a lower layer under the top layer of the laminated absorbent sheets.9. An absorbent article comprising an absorbent including a liquidpermeable surface sheet positioned on an inner side with respect to awearer's body in a wearing state; a liquid impermeable sheet positionedon an outer side from the surface-sheet; and an absorbent membercontaining super absorbent polymer particles as a major componentdisposed between the surface sheet and the liquid impermeable sheet,wherein the liquid distribution unit according to any one of claims 1 to7 is disposed in a position between the wearer and the absorbent member.10. The absorbent article according to claim 9, wherein the absorbentmember contains at least 50% by weight of the super absorbent polymerparticles.
 11. The absorbent article according to claim 9 or 10, furthercomprising a liquid permeable nonwoven fabric further disposed on theliquid distribution unit.
 12. The absorbent article according to any oneof claims 9 to 11, wherein the liquid distribution unit has an area ofat least 10 cm², the area is selected such that the ratio of the area tothe total area of the surface sheet is in a range of 5% to 50%, andaccordingly the liquid distribution unit is disposed so as to partiallycover the surface sheet.
 13. The absorbent article according to any oneof claims 9 to 12, wherein the liquid distribution unit is partiallydisposed only in a part of the surface of the surface sheet, and aliquid permeable nonwoven fabric is disposed only on the liquiddistribution unit.
 14. The absorbent article according to any one ofclaims 9 to 13, further comprising an acquisition layer disposed underthe liquid distribution unit.
 15. The absorbent article according to anyone of claims 9 to 13, further comprising a diffusion layer disposedunder the liquid distribution unit.
 16. The absorbent article accordingto any one of claims 9 to 13 further comprising a liquid impermeablesheet disposed under the liquid distribution unit in order to partiallyblock movement of the liquid into the absorbent member.
 17. Theabsorbent article according to any one of claims 9 to 16, wherein theabsorbent member has a retained absorption amount of 300 cc or more, awater absorption speed of 60 sec or less in each of three measurementsof the absorption speed performed every 100 cc at an interval of tenminutes, and a deviation of 30 sec or less among the three measurements.18. The absorbent article according to any one of claims 9 to 17,wherein the absorbent member is constituted of a absorbent sheetincluding any of a nonwoven substrate, super absorbent polymerparticles, and a microfibrillated cellulose.
 19. The absorbent articleaccording to any one of claims 9 to 17, wherein the absorbent member isconstituted of a absorbent sheet selected from the group consisting of awood pulp obtained by an air-laid method, super absorbent polymerparticles, and a binder.
 20. The absorbent article according to claim 18or 19, wherein the absorbent sheet has such a shape that opposite sideportions are bent to have a Z-shaped transverse section, and the liquiddistribution unit is disposed only in a center portion of the topsurface of the absorbent sheet.